> -----Original Message----- > From: IBM Mainframe Discussion List > [mailto:[EMAIL PROTECTED] On Behalf Of Rick Fochtman > Sent: Wednesday, April 09, 2008 10:36 AM > To: IBM-MAIN@BAMA.UA.EDU > Subject: Re: Sequential Data Striping > > > -------------------<snip>--------------------- > There's nothing wrong with stripes over stripes. I've > referred to this > as braiding in the past. > > With a good pre-fetch algorithm the storage uses the > parallelism of the > striped arrays to feed the cache in large block requests from many > disks, and in turn the RAID-0 dataset can feed the sequential read > process by pre-fetching from many concurrent volumes and paths. > > Braiding is a good thing. It is heavily used in UNIX land, > Not so common > on Windows, and unfortunately (for some unknown reason) > strangely rare > in MVS. > ------------------<unsnip>-------------------- > At the risk of sounding obtuse, I have to ask the question: why is > striping even an issue today? > > Given the architecture of modern "DASD-like" storage systems and the > advent of Dynamic PAV, the hardware and operating system > facilities SEEM > to address all of the performance considerations that might seem to > mitigate in favor of striping. > > ----------------------------------------------------------------------
There is one left. Even if the data is physically striped on the DASD, when you read an unstriped, in z/OS's view, disk dataset, you do a single I/O operation. If you use z/OS striping, you do multiple I/Os (one to each stripe), which hopefully means that you wait less for the I/O operation. The same on a write. I.e. the amount of data concurrently transferred is greater. Of course, if you have my luck, each stripe (z/OS DASD volume) will end up being on the same physical back end DASD and nothing will be prefetched in cache either. "If it weren't for bad luck, I'd have no luck at all." -- John McKown Senior Systems Programmer HealthMarkets Keeping the Promise of Affordable Coverage Administrative Services Group Information Technology The information contained in this e-mail message may be privileged and/or confidential. It is for intended addressee(s) only. If you are not the intended recipient, you are hereby notified that any disclosure, reproduction, distribution or other use of this communication is strictly prohibited and could, in certain circumstances, be a criminal offense. If you have received this e-mail in error, please notify the sender by reply and delete this message without copying or disclosing it. ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
